The present invention relates to an optical network tester shaped to be interchangeable with a complementary connector or generic fiber termini that intermates with an optical connector having both an optical emitter and an optical detector. The optical network tester comprises an alignment fixture having a pair of connectors or alignment ferrules for intermating it with the optical emitter and the optical detector.
The foregoing alignment fixture includes an optical fiber formed in a loop and installed within the alignment fixture with a first end face of the loop aligned through a corresponding alignment ferrule with an emitter, and a second end face of the loop aligned through a corresponding alignment ferule with the detector of the optical connector. In accordance with the present invention, a controlled air gap is added to the optical fiber loop to provide a desired level of attenuation.
It is known in the art to provide an optical network tester of the type generally described above, including the use of an optical fiber loop mounted in an alignment fixture. However, a desired level of attenuation is normally provided by use of a piece of filter glass which may be mounted on the end face of one of the above-mentioned alignment ferrules. Such an optical simulator is described in U.S. Pat. No. 4,982,083.
The foregoing patent shows in FIG. 1 a simulator 10 which is interchangeable with a complementary connector 7 for insertion into a transceiver adapter assembly 6 which includes an optical transmitter 2 and an optical receiver 3. As shown in FIG. 3 of the '083 patent, the simulator 10 includes an optical fiber 11 formed in a loop and having one end located in an alignment ferrule 23 facing an optical detector 5 and having its other end located in an alignment ferrule 24 facing an optical emitter 4.
As best shown in FIGS. 4A and 4B, the '083 patent discloses means of providing a desired level of attenuation comprising a square of filter glass 43 which is mounted on the end face 37 of the alignment ferrule 23. By thus attaching the filter glass 43 at one end of the optical fiber loop which faces the detector 5, the filter glass affords the desired attenuation of optical power to the optical detector.
Referring again to FIG. 1 of U.S. Pat. No. 4,982,083, in the testing of the optical transmitter 2, it is an object to determine whether the transmitter is transmitting an amount of light consistent with the required specifications for the transmitter, and such light output will be measured at the receiver 3. However, rather than plugging in the connector 7 and transmit through the cables 8 and 9 and check at the other end of the system, it is advantageous to utilize the simulator 10 in such a manner that the fiber loop 11 simulates the attenuation which would be achieved if the connector 7 and cables 8 and 9 were utilized. Thus, the object of such a simulator 10 is to check the dynamic range of the equipment, which is the amount of optical power transmitted by the emitter, and the simulator 10 serves the purpose of simulating the loss or attenuation in the system including the cables 8 and 9.
One significant disadvantage of the device disclosed in the '083 patent is the use of the filter glass shown at 43 in FIGS. 4A and 4B to provide the desired attenuation. Such a small square of filter glass must be microscopically applied to the end of the fiber optic alignment ferrule and, after precisely locating the filter glass, it must be bonded in position. However, if any movement of the filter glass relative to the fiber optic end occurs during the bonding procedure, such movement can vary the amount of attenuation caused by the filter glass.
In using a filter glass as taught by the above-mentioned '083 patent, there are two critical factors which affect the level of attenuation. One factor is the precise thickness of the filter, and the other factor is the precise location of the filter relative to the end of the fiber optic. As a result, it is necessary to use different filters to achieve different levels of attenuation. In addition, a very delicate operation is involved in bonding the tiny filter on the end of the alignment ferrule in a precise position relative to the fiber optic to achieve the expected level of attenuation.